CNIM Electromyography (EMG) and Nerve Monitoring 2 — Questions and Answers
Question 1: Which anesthetic consideration is MOST important for free-running EMG monitoring to be reliable?
- High-dose opioid infusion
- Avoidance of neuromuscular blocking agents after intubation (Correct answer)
- Use of volatile anesthetics only
- Deep hypothermia
Correct answer: Avoidance of neuromuscular blocking agents after intubation
Neuromuscular blocking agents prevent muscle response to nerve root irritation, making free-running EMG completely unreliable; only short-acting NMB for intubation is acceptable.
Question 2: The S1 nerve root is best monitored using EMG from which muscle?
- Tibialis anterior
- Iliopsoas
- Gastrocnemius and abductor hallucis (Correct answer)
- Quadriceps
Correct answer: Gastrocnemius and abductor hallucis
The gastrocnemius and abductor hallucis are primarily S1-innervated muscles and are the best myotomes for EMG monitoring of S1 nerve root integrity.
Question 3: During anterior cervical spine surgery, EMG monitoring of which muscle is most useful for detecting C5 nerve root injury?
- Biceps brachii
- Deltoid (Correct answer)
- Triceps brachii
- Hand intrinsics
Correct answer: Deltoid
The deltoid is the primary C5 myotome muscle and is most sensitive for detecting C5 nerve root injury, a common complication of anterior cervical decompression.
Question 4: Pop and burst EMG patterns during free-running monitoring are considered:
- High-risk patterns equivalent to neurotonic trains
- Lower-risk, brief responses to transient mechanical contact (Correct answer)
- Signs of complete nerve transection
- Artifacts from the electrocautery device
Correct answer: Lower-risk, brief responses to transient mechanical contact
Pop and burst patterns are brief, transient EMG responses to mechanical contact (touching the nerve) that are lower risk than sustained neurotonic trains but still warrant alerting the surgeon.
Question 5: Which recording parameter is critical for obtaining accurate EMG recordings from muscles intraoperatively?
- Electrode impedance below 5 kΩ (Correct answer)
- Filter settings of 0.1–1 Hz
- Use of surface electrodes only
- High-pass filter set above 3000 Hz
Correct answer: Electrode impedance below 5 kΩ
Electrode impedance below 5 kΩ is required for reliable EMG recordings to ensure adequate signal quality and minimize electrical noise contamination.
Question 6: Electrical interference from the surgical cautery (electrosurgery unit) in EMG recordings is best managed by:
- Increasing the filter high-frequency cutoff
- Having the surgeon temporarily stop cautery, noting the artifact, and confirming it does not persist after cessation (Correct answer)
- Using a lower stimulation rate
- Increasing amplifier gain
Correct answer: Having the surgeon temporarily stop cautery, noting the artifact, and confirming it does not persist after cessation
Electrocautery produces intense artifact; communicating with the surgical team to pause cautery use when EMG activity is observed confirms whether the activity is artifact or genuine nerve activity.
CNIM Electromyography (EMG) and Nerve Monitoring 2
Which anesthetic consideration is MOST important for free-running EMG monitoring to be reliable?